Twitter turns 7 on Thursday, and here's a wish to wish while blowing out the candles: Would someone explain why, given the slew of highly publicized cases of embarrassing, self-destructive or career-ending uses of social media, people keep shooting themselves digitally in the foot?

Exhibit A is Steubenville, Ohio, where graphic tweets and posted photos and video helped convict two high school football players of raping a 16-year-old girl. That was Sunday; the next day, two girls were arrested and accused of making online threats against the accuser and victim.

It was merely the latest evidence that an immutable law of human nature and a key to human survival — we learn from our mistakes — seems to have been suspended online.

Dave Kerpen is CEO of Likeable Media, a social media marketing firm. "My hope is that people will learn, and I wish I could say that they are," he says. "But if anything, we're seeing more and more of this foolishness. I don't see it going away."

That's because the problem is not the technology, says Steve Rubel, chief content strategist for Edelman public relations. It's us.

"The technology just magnifies what's already there. It's an accelerant. Social media hasn't dramatically altered human behavior, it just makes it more apparent. If you incriminate yourself, it's more discoverable, more distributable and more embarrassing."

Social media are an indispensable megaphone for the famous — if they use it responsibly — from newly installed Pope Francis to President Obama to Tiger Woods and Lindsey Vonn, who used it this week to announce they were in a relationship — and to ask for privacy. For the rest of us, it's a convenient way to stay in touch.

But no matter how many people learn their lesson about online safety — personally or vicariously — so many new users pour onto the Internet each month that public education always lags behind practice.

Twitter, for instance, now counts more than 400 million tweets a day, compared with about 340 million a day a year ago; 32 million at the beginning of 2010; and 2 million a year before that.

How many tweets a day?

The micro-blogging service started out with just over 5000 tweets a day in 2007 but today claims over 400 million a day.

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tweets per day (in millions)

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And these users are disproportionately young — in many cases more adept technologically than socially, especially outside an immediate circle of peers. Those most fluent in the new social technology are often least aware of its potential dangers.

Of course, every new technology (Facebook is two years older than Twitter, the photo sharing service Instagram four years younger) takes us time to master.

Early telephone users had to learn how begin the conversation — the use of "Hello!" has been attributed to Edison himself — and how to end it. (At first, some people simply hung up when the conversation lagged.)

It all helps explain the steady stream of new social media horror stories — what folklorists call "cautionary tales" — that are supposed to be self-limiting.

Since the perilous cave days, humans have used such stories to teach survival lessons. Classically, there's a threat (say, fire); a taboo (children shouldn't play with matches); a violation (child plays with matches); and a result, often grisly (child sets himself on fire).

With social media, the problem is clear: Good, old-fashioned stupidity has become publishable, distributable, retweetable, immortal. Kerpen frames the dilemma this way: "Social media is here to stay, and foolish is here to stay."

Such was the case in Steubenville. Alexandria Goddard, a 45-year-old web analyst and former Steubenville resident, focused attention on the case by digging up photos and texts sent on the night of the attack.

"It is one thing to hear the rumors, but I think when people actually saw the tweets, and the vile things that were said, with their own eyes, it really drove home just how disgusting the behavior of these kids was," she wrote in her blog this week.

The texts introduced at the trial included those in which one of the students, Trent Mays, admitted to digitally penetrating the girl. In other messages, he told friends he'd participated in a different, mutual sex act with the girl. He also sent messages to friends asking them to cover up what happened. In one text he asked, "Just say she came to your house and passed out."

POLITICAL CAREER IMPLODES

U.S. Rep. Anthony Weiner announces his resignation from Congress, in Brooklyn, N.Y., on June 16, 2011. Weiner said he cannot continue amid the controversy surrounding sexually explicit messages he sent to women on Twitter.(Photo: Richard Drew, AP)

The great social media cautionary tale is Anthony Weiner's. The sharp, articulate Democratic congressman from Brooklyn was on his way to becoming mayor of New York City until two years ago when he accidentally used his public Twitter feed (as opposed to a direct message) to send a female Twitter follower (other than his wife) a link to a photograph of his bulging underwear.

Weiner has lots of company.

Some online mistakes are merely embarrassing, like last September when actress Alison Pill of HBO's The Newsroom posted a topless photo intended for her boyfriend's eyes, to her Twitter account.

Some are costly. Comedian Gilbert Gottfried was the voice of the Aflac duck in commercials until he joked about the Japanese tsunami on Twitter ("Japan is really advanced. They don't go to the beach. The beach comes to them.").

Some are final. Actress Nicole Crowther, an extra on the TV series Glee, tweeted some plot spoilers two years ago, to which producer Brad Falchuk tweeted "Hope you're qualified to do something besides work in entertainment."

Sports figures feature prominently in the Twitter doghouse. They include former Chicago White Sox manager Ozzie Guillen, who was suspended for two games after tweeting protests about an umpire who threw him out of a game.

But Guillen shows you don't need Twitter to put your foot in it. He has also done it the old-fashioned way, calling then-Chicago Sun-Times columnist Jay Mariotti a gay slur, defending illegal immigration on the basis that Americans are "lazy;" and saying he loves Fidel Castro — a comment in an interview with Time that got him suspended for five games.

LEGAL ISSUES ARISE

Sometimes tweeters have the law on their side.

This week three Indiana girls whose Facebook posts last year, featuring smiley faces and "LOLs," discussed which classmates they'd like to kill, reached a settlement with the school district that expelled them.

The girls, who were ousted in eighth grade, returned to Griffith Public Schools for their freshman year of high school last fall. They said they were joking.

The posts were made after school on the girls' personal electronic devices and were visible only to those whom the girls had allowed access. The terms of the settlement were not disclosed.

The U.S. Supreme Court has generally ruled that students have free-speech rights, and schools can prohibit their speech only if it is vulgar or disruptive to schoolwork or other people. The lawsuit says the posts did not cause any disruption at school.

Kerpen says one group does seem to have taken the warnings to heart: politicians. "Anthony Weiner scared a lot of them," he says. "Some of them still won't use Twitter themselves."

RULES TO LIVE BY

The better idea, Kerpen says, is to know what you're doing online.

To that end, here are two rules for protecting your online reputation:

1. When online, you're your own PR person.

Rubel, the Edelman strategist, offers this free advice: When online — Twitter, Facebook, Instagram, whatever — "You need to realize that your image is shaped by what you share."

Actually, he says, many people get this, if only subconsciously; what they share is designed to make themselves look good, especially among peers. The problem, he says, is "some people are not self-aware" and don't consider non-peers.

One result: The office worker who, having called in sick, posts to Facebook a photo of himself drinking beer out of a barrel-size red plastic cup.

Another result: Tweeters who think they're tweeting only to confidants but wind up on the Twitter account @YesYoureRacist, which is designed to out racist tweets.

"If mom doesn't mind that you're a racist or an idiot or an exhibitionist, go ahead," he says.

And don't be lulled into a sense of complacency by Twitter's 140-character format, which can seem so quick and easy — and be so costly. A woman named Connor Riley, upon receiving an offer from Cisco in 2009, tweeted: "Now I have to weigh the utility of a fatty paycheck against the daily commute to San Jose and hating the work." Unfortunately, someone at Cisco was reading.

What social media may need is a credible, recognizable spokesman for online sensibility, someone like Smokey the Bear: "Only you can prevent cyberflubs!"